Internet-of-Things (IoT) is the vision of virtually all objects being connected to the internet, where the objects can be anything from simple sensors to sophisticated machinery, such as vehicles. The Third Generation Partnership Project (3GPP) is currently specifying a new kind of radio access technology (RAT) with strong commonalities with Long Term Evolution (LTE) but operating over a narrower bandwidth. The new RAT is referred to as Narrow-Band IoT (NB-IoT). Specification work is currently ongoing, and the following decisions regarding deployment scenarios and duplex modes, downlink channels and signals, uplink channels and signals, and channel raster, were made at the 3GPP RAN1#83 meeting in November 2015.
Regarding deployment scenarios and duplex modes, three deployment scenarios were specified:                standalone deployment;        deployment in guard band between conventional LTE cells; and        deployment within the band of conventional LTE cells.        
Both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes are in the scope but are covered in different releases (e.g., FDD is in Release 13 but the solution shall be forward compatible with TDD which is introduced in a later release).
Regarding downlink channels and signals, the downlink subcarrier spacing is proposed to be 15 kHz and the NB-IoT downlink system bandwidth is proposed to be 200 kHz, with an efficient bandwidth of 180 kHz (e.g., the equivalent to a physical resource block in a conventional LTE cell). Two configurations for cyclic prefix (CP) are considered: normal and extended. FIG. 6 shows an exemplary downlink resource grid (in a time-frequency representation) for a Normal Cyclic Prefix (NCP) and for an Extended Cyclic Prefix (ECP), where the shaded areas indicate where NB-IoT-specific synchronization signals may be scheduled. The number of transmission ports used by the network node is assumed to be one or two, where for the latter, Space-Frequency Block Coding (SFBC) is assumed. The NB-IoT-specific channels that have been specified to some extent are the broadcast channel (NB-PBCH), the downlink control channel (NB-PDCCH or NPDCCH), and the downlink shared channel (NB-PDSCH). It shall be noted that the nomenclature is not finalized, but the indicated names are used here to distinguish the channels from their counterparts in regular LTE cells. System information is provided via a master information block that is transmitted on the NB-PBCH and for which format and allocation is known in advance, and via system information block(s) that are transmitted on NB-PDSCH.
Further, new synchronization signals, e.g., NB Primary Synchronization Signal (NB-PSS or NPSS) and NB Secondary Synchronization Signal (NB-SSS or NSSS), are Introduced, with, e.g., a single instance of NB-PSS and 504 instances of NB-SSS. The synchronization signals occupy a fixed number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in each subframe that is carrying synchronization signals.
The synchronization signals do not occupy the first three OFDM symbols in the subframe, and for the scenario where NB-IoT is deployed in the bandwidth of a regular LTE cell, Cell-specific Reference Signals (CRSs) of that regular LTE cell will puncture the NB-PSS or NB-SSS if necessary. For NCP, it is assumed that the NB-PSS and NB-SSS span nine or eleven OFDM symbols (to be down-selected to one value), and that within the span six to eleven OFDM symbols carry the synchronization information (to be down-selected to one value). For ECP, the corresponding figures are nine OFDM symbols and six to nine OFDM symbols, respectively. For the in-band scenario, NB-PSS and NB-SSS are boosted by 6 dB relative to the cell-specific reference signal (CRS) power level in the regular LTE cell. The repetition rates of NB-PSS and NB-SSS might differ. For example, repetition rates of 20 ms and 80 ms, respectively, have been proposed.
Regarding uplink channels and signals, two solutions are proposed for uplink transmissions: single-tone transmissions using either of two configurations, e.g., 3.75 kHz and 15 kHz bandwidth, and multi-tone transmission using 15 kHz subcarrier spacing in a Single Carrier Frequency Division Multiple Access (SC-FDMA) scheme. Details regarding uplink signals are still under investigation.
Regarding channel raster, the channel raster is assumed to be 100 kHz although sparser channel raster cannot be precluded as it is still under discussion in the standardization body.
Current LTE solutions either operate at a sampling rate that may undesirably increase the financial and/or power costs of the corresponding devices, or operate at a cost-efficient sampling rate that undesirably degrades performance. Reducing that sampling rate, however, may negatively impact uplink transmission timing. Therefore, there remains a need for improved processing and timing solutions, particularly for NB-IoT devices.